On the Anniversary of Ernest Rutherford’s Find

“In 1907, a New Zealander named Ernest Rutherford moved from McGill University in Canada to the University of Manchester. There, he conducted a series of experiments where he fired alpha particles at different materials,” Vasudevan Mukunth writes for Indian news website, The Wire.

“When [Rutherford] found that the beams deviated by about 2º when fired through air, he figured that the atomic constituents of air would have to have electric fields as strong as 100 million volts per cm to explain the effect,” Mukunth writes. “Over the next decade, Rutherford – together with the help of Hans Geiger and Ernest Marsden – would conduct more experiments that ultimately resulted in a very important result in the history of physics: that the atom was not indivisible after all.

“In the last year of the 19th century and the first year of the 20th, Rutherford, and Paul Villard, had independently isolated and classified radiation into three types: alpha, beta and gamma. Their deeper constituents (as we know them today) weren’t known until much later, and Rutherford played an important role in establishing what they were. By 1911, he had determined that the atomic had a nucleus that occupied 0.1 per cent of the total volume but contained all the positive charge – known today as the famous Rutherford model of the atom. In 1914, he returned to Australia on a lecture tour and didn’t return to the UK until 1915, after the start of World War I. Wartime activities would delay his studies for two more years, and he could devote his attention to the atom once more only in 1917.

“That year, he found that when he bombarded different materials with alpha particles, certain long-range recoil particles called ‘H-particles’ (a term coined by Marsden in 1913) were produced, more so when nitrogen gas was also present. This finding led him to conclude that an alpha particle could have penetrated the nucleus of a nitrogen atom and knocked out a hydrogen nucleus, in turn supporting the view that the nuclei of larger atoms also included hydrogen nuclei. The hydrogen nucleus is nothing but the proton. Rutherford couldn’t publish his papers on this finding until 1919, after the war had ended. He would go on to coin the term ‘proton’ in 1920.

“One hundred years after the proton was first sussed out, particle physics itself looks very different from the way it did in Rutherford’s time, and a large part of the transformation can be attributed, one way or another, to the proton. Today, physicists pursue other, very different particles, dream of building even larger proton-smashing machines and are busy knitting together theories that describe a world much smaller than the one of quarks and gluons. It’s a different world of different mysteries, as it should be, but it’s also great that there are mysteries at all.”